Voice over Internet Protocol (VoIP) involves the routing of voice conversations over the Internet or other packet switched networks. Calls can be made over the Internet using an IP phone, which is a phone that uses VoIP technology. VoIP provides a secure form of communication by using existing encryption and authentication protocols, such as the Secure Real-time Transport Protocol (SRTP). Most of the difficulties of creating a secure communication over traditional phone lines, like digitizing and digital transmission, are already in place with VoIP. Only the additional steps of encrypting and authenticating the existing data stream are required.
VoIP networks are increasingly used as alternatives to the public switched telephone network (PSTN). VoIP systems allow companies to extend communications services to all employees, whether they are in office headquarters, at branch offices, working remotely, or even working mobile. Also, being software based, VoIP systems are highly scalable. A typical VoIP system, for example, can handle anywhere between 1 and 10,000 users. VoIP's scalability is especially useful for fast-growing companies or those that must respond quickly to changes in demand.
Another benefit of being software based is that most VoIP systems include features for which telecommunications companies using the public switched telephone network (PSTN) normally charge extra. Some examples include 3-way calling, call forwarding, automatic redial, caller ID, call waiting, voice mail, conference calling, call transfer, and others. In addition, some VoIP providers offer features that are not available from traditional telecommunications companies. For example, a general purpose desktop computer, or soft phone, may be used to make telephone calls over the Internet. Also, some VoIP providers offer a “soft” client that allows a user to control calls from a desktop computer. Such a system includes the ShoreTel Personal Call Manager from ShoreTel, Inc. of Sunnyvale, Calif. These are just some of the unique features that providers of VoIP systems can offer.
Despite the array of features possible from a VoIP system, there are often challenges in incorporating even those features that are common with the features offered by traditional telecommunications companies. A simple example is making emergency phone calls. With the mobility enabled by being Internet-based, it may not be possible to determine the geographic location of a user in a VoIP system. If a caller's geographic location can not be determined, emergency phone calls cannot be routed to nearby call centers. Another example is sending faxes. Existing voice codecs are not designed for fax transmission.
Yet another feature that may not incorporate seamlessly into a VoIP system is overhead paging. An overhead paging system is often used in large department stores to “page” employees or in airports to make announcements. Traditionally, these systems included an analog phone with the speaker wired directly to the various speakers of the system. A person uses such a system by dialing the number of the phone, the phone auto-answers, and when the person talks his or her voice is broadcast over the speakers of the system.
Overhead paging can be incorporated into a VoIP system in a manner analogous to that of a traditional overhead paging system, by using an IP phone or soft phone with the speaker wired directly to the various speakers of the system.
VoIP systems, however, offer other advantages. For example, VoIP systems can play a voice message over the speakers of a group of IP phones or soft phones without requiring anyone to take the phones offhook. This allows a voice message to be sent concurrently to users at different locations, and is not limited by the range of the speakers wired to the system. A voice message can be delivered through the speakers of phones in different buildings that may be in different parts of the country. Further, some VoIP systems allow users to create custom groups of phones to which voice messages are sent. For example, a company with several different departments may create a custom group for voice messages that are sent to one department, another custom group for voice messages that are sent to a particular combination of departments, another custom group for voice messages that are sent to all departments, and so on.
However, there are challenges to realizing these benefits. For example, playing a voice message over the speakers of individual phones requires that a connection be established with each phone. Differences in the time it takes to establish each connection results in the message playing from phones at different times. If the phones are in close proximity to one another, a listener may experience an echo. An echo results when the sound comes from the speakers of different phones at different times. Echo can make voice messages difficult to understand.
Traditional overhead paging systems did not have a problem with echo because the speakers of the system were wired directly to a single phone. In terms of listener perception, messages were delivered from the various speakers at the same time. However, delays are more likely in VoIP systems since they rely on packet switched networks to setup connections with each phone. Despite the additional features enabled by a VoIP system, users require the basic functionality of the system to be at least equal to traditional systems. Like traditional overhead paging systems, VoIP systems must deliver voice messages such that any delay is unperceivable. At least to human perception, the message being played from the different phones must be synchronized.
One method that has been used to ensure that voice messages processed through VoIP systems are synchronized is to record the messages and delay sending them until after the entire message is recorded. However, this solution is unsatisfactory to users who generally want their voice messages to be played virtually real time.
Thus, there is a general need in the art for an improved method and apparatus for playing voice messages that are processed through a VoIP system.